How Do Clouds Affect Earth's Climate?

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Some clouds help cool the Earth, but other clouds help keep Earth
warm – in part depending on how high up they are in our
atmosphere. That’s according to Steven Platnick,
a satellite researcher with NASA. He studies clouds and how they
connect with Earth’s climate. He said that low, fluffy clouds
keep us cooler.

SP: You can appreciate that if you go out on a
hot and sunny day, and a cloud passes by overhead, it’s a great
relief from the heat. And the reason of course is because the
cloud is reflecting sunlight.

But it’s a different story for clouds that are high up in the
atmosphere, said Platnick. Those high, wispy clouds actually keep
Earth warm, like a blanket, by preventing heat from escaping into
space. Platnick uses NASA’s Aqua satellite to determine
the height of clouds, and other properties of clouds as well --
like what’s inside them, how much water they have, and whether a
cloud is primarily liquid or ice. The satellite also tracks the
amount of cloud cover all over the world.

Steven Platnick: The most important thing to
trying to understand their effect on global climate is we need to
know how they’re globally distributed and how they vary over the
course of a year. And you need satellites to really obtain the
statistics over those scales. It’s really impossible for most of
those quantities to get the same statistics from ground-based or
aircraft observations.

Platnick explained to EarthSky what scientists mean when they
talk about climate.

SP: When scientists talk about climate, what
we’re talking about is the statistics of weather. And normally
we’re talking about that on multi-decadal time scales, and
longer, even centuries and millennium. An example might be the
average surface temperatures, something that most people can
relate to. Or also, the minimum and maximum surface temperatures.
And there’s other examples -– precipitation, the amount of
rainfall during the month, or snowfall, or snow pack. But when we
talk about recent climate change, and the causes of recent
climate change, and that’s over the last several decades
including the last several centuries since the start of the
industrial revolution, then we start to study the effect of human
activities, and how humans can directly modify climate.

Platnick said that there are several ways that humans can
directly impact climate. The best understood of these, he said,
and what’s likely the most important in the long run, is the
release of greenhouse gases into the atmosphere.

SP: And that includes not just carbon dioxide,
but methane, ozone, there’s other gases as well. And these
greenhouse gases perturb the radiation balance of climate. And
what they do is move the climate system to a warmer state. And it
does that because of the way that gases reduce the emissions of
infrared radiation to space by the Earth and its atmosphere. And
this so-called greenhouse gas forcing on the climate system is
well-understood.

He said that what’s less well-understood is how the climate
responds to this forcing.

SP: And that is the focus of much climate
modeling research today. It’s certainly the motivation behind
many of NASA’s satellite observations and the modeling studies
that we do, and that’s in fact what a large part of my own work
involves.

Platnick told EarthSky what he thought was the most important
thing people should know about Earth’s clouds and climate.

SP: Earth is a dynamic system of components. On
the largest scales you have the atmosphere, the land, the ocean,
snow and ice on the ground. And these systems connect with each
other in different ways, through the exchange of water, and
energy, and chemistry, such as the exchange of carbon. We need to
be able to better understand the consequences of these
connections. Clouds are the prime example of this
interconnection, because they play a key role in these systems,
especially in the water and energy connections.

NASA satellites and instruments, along with our
international partners are helping us to get better observations
we need to understand these cloud physical processes and to
enable cloud model improvements as well.